Brakes G60's vs UFO's and other combos............

Dan Cordon cord4530 at
Tue Feb 17 02:51:08 EST 2004

>>I'm no brake engineer, but I
>>> theorize that if I compare two like kind setups braking with the ABS working
>>> and then not engaging the ABS by modulating the brakes at threshold, I'll bet
>>> the ABS will have a longer stopping distance leading to less heat generated on
>>> the brake rotor and its components.
> Not so!  Its the same amount of kinetic energy being converted into heat,
> independent of the braking system.

Actually, Scott's right on this one. While it *is* the same amount of 
energy (at least for all practical purposes), the energy is converted in 
a shorter amount of time -- meaning more power. Power is a rate of 
energy flow.

>>The brakes convert car velocity movement into kinetic heat into the rotor
>>> during stopping.  The result is, you have generated more brake heat in a
>>> shorter braking distance.
> Your terminology is so screwed up that who is to question?

In this case, that's not quite right. WE could say that brakes convert 
kinetic energy (from vehicle velocity) in to thermal energy by friction. 
But there is  no more heat generated by stopping faster than stopping 
slow. But since the power is greater, the brake component temperatures 
will be greater.

Still, this is a pretty small difference in time between ABS stopping 
and threshold stopping, so the power difference is probably negligible.

I remember when ABS was becoming more common, that most published 
numbers for stopping distance reported that stopping with ABS took 
longer than w/o ABS engaging. However, in more recent magazine articles 
this seems to have switched. Aside from tire lockup w/o ABS, I can't see 
how a car would stop faster with ABS engaged.

Anyone else notice this?

Dan Cordon
Mechanical Engineer - Engine Research Facility
University of Idaho

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